Fighting fire risk

Published: 02 July, 2014

ODEE spoke with Thomas Götz, fire safety & security head for the Northern Region at Siemens Building Technologies, about Siemens’ recently launched automatic fire-extinguishing system for offshore wind turbines, and about the wider issues surrounding fire prevention.

Siemens Building Technologies has introduced an automatic fire-extinguishing system for offshore wind turbines, designated the Active Fire Fighting System (AFFS). Its most publicised installation to date is that on the Riffgat project in the German North Sea. Thomas Götz from Siemens Building Technologies explained that the system has been designed to reduce the risk of damage to the machines while also limiting the threat to the lives of personnel working on the turbines.

The Active Fire Fighting System (AFFS) uses intelligent fire detectors to alert the system to a fire in the nacelle or tower. This then activates a nitrogen gas extinguishing system to put out any fires, operating on the principle of oxygen displacement. The oxygen content in the area is diluted by nitrogen until a non-explosive, non-flammable environment is created. The inert gas leaves no residue behind. The fire-detection system continuously sends status messages to a control station. From here the turbine is shut down automatically by its controller or, if necessary, by operators. To enhance safety, one system is installed in the nacelle and one in the tower base. These two systems are interconnected but operate autonomously in the event of a network outage or power failure.

Götz provided the background to the development of the system. “We were asked by several wind turbine manufacturers that equip offshore wind parks in the North Sea and the Baltic Sea to design a tailored firefighting system for their wind turbines. By tailored, I mean it’s not a traditional-type component that simply plugs into a turbine. Therefore we needed to dedicate much of our design and engineering resources over quite a long length of time to looking closely at all the potential fire risks and hazards on wind turbines, together with the probability of occurrence or the likelihood of damage as well as possible consequential losses in terms of downtime etc.”

Subsequently Götz and his team set about analysing the complete risk chain. “First, we looked at the overall topology and architecture of typical wind turbines and then began designing the system,” explained. “Then, this general design phase was followed by the prototype phase. Here we produce two or three prototypes which are then initially erected on onshore turbines. This is because of course it’s easier to control and install in the early stages of development than it would be to fit the fire extinguishing system to an offshore turbine in the first instance.”

Götz explained that the Siemens Building Technologies then ran a series of fire tests to ensure the integrity of the system design. “Of course, at this stage local fire brigades and insurance companies needed to be informed,” he said, “Once AFFS had been thoroughly tested it then received both the land-based VDS certification – which is comparable to the LPCB in the UK – and German Lloyds approval for offshore applications.”

The new fire extinguishing system consists of three main parts: fire detection, fire extinguishing and communication. Götz elaborated: “In terms of detection, you need to be able to control the heat of the transformer in the turbine to make sure that before the transformer explodes you know in advance that it’s about to happen due to the monitoring of the increase in temperature. You also need to ensure that the oil hubs are monitored by flame detectors so that any spark that occurs due to an emergency ‘hard-stop’ is detected early enough. Also important is that smoke and heat detectors should be tailor-made to the specific type of cabinets used on different wind farm applications, and that there should be forced air ventilation in the cabinets to make sure that there is the best chance to see that the air ventilation is blowing smoke out before you would otherwise have the chance to see it.”

On the extinguishing side, Götz explained that the system can be tailored to suit the specific types of fire risks on different wind turbine applications. “For example, if an oil-based or liquid-based fire occurs, different extinguishing means are required than would be the case if, say, a paper-based fire broke out. In the case of a paper-based fire water would be the extinguishing agent, whereby in the case of an oil or liquid-base fire a foam agent is required. Therefore different extinguishing agents are needed for the different types of turbine with different fire risks.”

The communication part of the system can be split into two subgroups. “The first is the communication with the overall turbine system,” explained Götz. “For instance, if a fire breaks out this communication part makes sure that the turbine is immediately shut down and put into a safe position.”

The second communication component provides complete remote diagnostics control and servicing. “All of the fire panels and detectors can be remotely accessed, controlled and even serviced from a remote control centre, which is either operated by the wind park operator, by the turbine manufacturer or by ourselves,” said Götz.

Extinguishing agent

And what of the most appropriate extinguishing agent for the system? “When selecting the most suitable type you need to be aware that some might have quite a high level of residue,” said Götz. “These residues are not generally liked by the operators because chemical reactions with other components can occur, or they might have an environmental impact, and a post-event dedicated cleaning regime is often necessary, which naturally takes time and costs money. This is why we select our extinction agents to be on the one side technologically effective while also being cost-effective – and also making sure that detection, extinguishing and communication are all taken care of by the technology behind the extinction system.”

In terms of the extinguishing foam used by Siemens Building Technologies for AFFS, Götz pointed out that the company uses its own solution. “This is another reason why many turbine manufacturers like to use our systems,” he remarked. “We don’t only act as a systems integrator sourcing third-party equipment and installing it onto the turbine, we manufacture our own products on the detection, extinguishing and communications side. This gives us a strong advantage in terms of equipment life-cycle considerations. With regard to spare parts, service and repair all this can be done in-house within our group of our departments, even down to the manufacturing – so we are effectively controlling the complete value chain.”

Maintenance requirements

In terms of the ongoing maintenance of the system, this type of work can be undertaken by Siemens Building Technologies personnel or sub-contracted to partners. “There are some wind park operators who like to have their own service force equipped and trained, and in that regard we are able to train these operators so they can do undertake the maintenance tasks themselves,” explained Götz. “We can also train the service groups of the turbine manufacturers to action maintenance tasks under our supervision.”

Götz added that all three maintenance strategy options are always based around the effective control and monitoring of the system. “For example, if you have an ideal opportunity to go out to an offshore application when weather conditions permit it is important that the service technicians already know what they should bring with them in terms of tools and spare parts etc. to take care of the problem. You definitely don’t want to go out there by helicopter and then realise you have forgotten a vital component.”

With this in mind, the Siemens’ ICBT control centre offers a free diagnosis service. “This can, for example, involve ensuring that a particular technician goes to turbine 27 and that he has one heat detector in spare as well as bringing another EMC basket which needs to be put on detector number five,” said Götz. “In this way, the technician knows from the outset precisely what work needs to be carried out on the turbines, calculate service execution trends and know exactly which items to bring with him. The technician also knows more accurately how much work is likely to be involved, and so can better determine whether there would be a need for a second technician for maximum time efficiency.”

Risk-factors

In terms of the risk factors that could potentially harm the end customer and result in a financial loss to the operator, fire is considered to be number two or three by insurance companies in the main, Götz pointed out. “This assessment is based largely on the fact that in a turbine – especially in some recently installed ones that are considerably larger than some of the older models – the electrical components are often densely populated. For example, if you look in an electrical cabinet in an average onshore building there is normally quite a lot of space between the different electrical components. Therefore the danger of arc generation of sparks is limited. If you look in an offshore wind turbine cabinet it is often so full of components that it can be hard to install any kind of fire detector inside. And this dense packing of components can increase the electrical fire risks.”

Götz added that there are also the thick metal plates where all the main current runs through to be considered, and the fact that high-voltage current bars made out of copper can be 5 cm thick often with high ampers running through them. “This can result in electromagnetic radiation issues, and so a fire could occur if a spark is produced by any of the cramped electrical components,” he said.

Then there are the transformers and the power units in many of the turbines. Even though the transformers are normally self-monitored, Götz points out that they can be a fire risk because they often run for 30 years without any interruption – and in general, the fire risks increase considerably after five years.

Also to consider, according to Götz, are the drive systems such as brakes, hydraulics and gears. “Over time, this equipment can leave a residue of oil dust and oil leakages that are collected in the oil hub below,” he explained. “And if you combine sparks with these oil residues then it is not difficult to understand the fire risks. There are also issues concerning oil motors and blade motors, although technological advancements have resulted in these now becoming a lower fire risk.”

The cost factor

If a fire does occur on a wind turbine, the commercial losses can be substantial, as Götz outlined: “If a turbine burns it is not only the loss of the turbine that’s the problem – and this can cost around 1.5 million euros in many cases – but much more severe is the waiting time until you have a new working turbine up and running. Most of the turbine manufacturers have full order books, and you will need to wait for the right weather conditions and have to dismantle the old one – all this takes time and money. Installing a new turbine can cost between 10 million and 20 million euros, then on top of this you have the incurred losses through not having generated any energy.”

“So,” continued Götz, “ all round, a fire can prove very expensive for the wind park operator, whereas an effective fire-extinguishing system such as AFFS can be purchased and installed for between 10,000 and 100,000 euros. And with the risk of fire dramatically reduced, it is no surprise that many insurance companies will happily reduce their premiums if you have such a system installed.”

In addition to the Riffgat offshore project and other pending offshore installations, Götz explained that Siemens Building Technologies is also looking to equip onshore wind turbines with the same types of benefits that AFFS affords their offshore counterparts. “Wind farm operators in Southern European countries such as Spain, Italy and Bulgaria are showing positive interest in this technology, and are looking to make investments,” he said. “Similarly, the Southern German region, Austria and Switzerland are about to see the erection of new wind turbines that are sufficiently high to reach into the non-turbulent wind areas. The owners of these projects are also showing interest in AFFS because the turbines are often placed in areas of dense forest. Here it makes perfect sense to install AFFS as well.”

Certification for AFFS

The Siemens AFFS fire detection and extinguishing system for offshore wind farms is certified by VdS Schadenverhütung GmbH and according to GL Renewables by Germanischer Lloyd. The AFFS is therefore officially approved for use as a safety system in offshore wind turbines. The AFFS concept was developed by the Siemens Building Technologies Division over a period of one-and-a-half years and the system was subsequently tested extensively in a pilot phase in Brande, Denmark and Flensburg, Germany. During the VdS certification process, experiments conducted in the VdS fire laboratory proved that the behaviour of the nitrogen in the extinguishing areas was fully stable. After certification, the first systems were installed in the Riffgat Wind Farm, northwest of the island of Borkum. The AFFS is used in thirty turbines installed by the Siemens Wind Power Division for EWE, a northern German energy provider, and Enova Energiesysteme, the project developer.

The Siemens Building Technologies Division (Zug, Switzerland) provides safe, secure, energy efficient and environmentally friendly technologies for buildings and infrastructures. As technology partner, service provider, system integrator and product vendor, Building Technologies has offerings for safety and security as well as building automation, heating, ventilation and air conditioning (HVAC) and energy management. The division has approximately 28,000 employees worldwide.